Method of heat treating magnet steels



Jam. 5, 3%2. K. L. scoTT ET AL METHOD OF HEAT TREATING MAGNET STEELS Filed Jan. 18, 1930 a M Mi w 3 MSKZ .W/ZR m 5/ J .me W 5 2H J Patented am. s, new

PATENT oFFea KENNETH 3L. SCOTT, OF WESTERN SPRINGS, ARTHUR L. KIRIBY, OF CICEBO, AND

MARION R. LEACE, OF CHICAGO, ILLINOIS, ASSIGNORS TO WESTERN ELECTRIC COK- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK METHOD OF HEAT TREATING -HAGNET STEM Application filed January 18, 1980. Serial No. senses.

This invention relates to a method of heat treating magnet steels, and more particular-' ly to a method-of improving the magnetic properties of cobalt magnet steel.

An object of the invention is to provide a method'whereby material improvements in electrical and magnetic properties may be imparted to magnet steels.

It is a well known fact that in the ordinary methods of heat treating magnet steel while the residual induction increases. Since these changes have, in the ordinary methods,

' occurred simultaneously, it has been assumed that they must occur simultaneously. However, this assumption has been proved incorrect in that the residual induction increases as before while the coercive force is stabilized, when thesteel is quenched in a heated medium of the proper quenching temperature.

drawing, in which the single figure is a time chart illustrating the subsequent relative c0ndition of the magnetic properties of the magnet steel.

This method consists in first heating a magnet steel, such as chrome steel, or cobalt steel containing 20% to 40% cobalt, to a uni form temperature of 17 50 F. The magnet steelis then qlqenched in an oil, salt, or other medium whic is maintained at a temperature higher than room temperature. The

temperature of-the'quenching medium ranges from 200 F. to 600 F. depending upon the magnet steel, as, for example, a cobalt steel containing approximately 36% cobalt is quenched in a medium having a temperature of 500 F. This quenching of the magnet steel in the. heated medium brings about a slow 'quenchingand consequently the magnet steel has very high coercive force.

Such a result is illustrated in the drawing, wherein the horizontal line 1 indicates time subsequent to the quenching of the magnet steel and is graduated according to .days. The vertical line'2 indicates the magnetizing force of the magnet steel according to gilberts per centimeter; The high and stable coercive force which is the result of the. slow quenching of the 36% cobalt'steel at a temperature of 500 F. is illustrated by line 3 showin a coercive force of ap roximately 275 WhlCh is retained stable. 'I he residual induction of the treated 36% cobalt steel is illustrated by the line 4 As is well known, high coercive forces are of particular advantage in permanent magnets, and with this method of improving the magnetic properties of the magnet steels not only exceptionally high but stable coerciveforces are imparted to the magnet steels. v

This specific example has been given as one embodiment of the invention, but other tests have been made wherein higher and stable coercive forces have been obtained. The heat- 7 treating temperature of 17 50 F. isthe preferred temperature for magnet steel containing 20% to 40 cobalt but the heat-treating temperatures may vary depending upon the metallic characteristics of the magnet steel being treated. During each heat-treatment of magnet steel the steel is heated to a temperature above the critical temperature, which of course varies with the composition of the material being treated. Furthermore, eventhough only two classes of steels have been disclosed, it should be understood that this .invention is not limited to only these two classes of steels, but may include any other steel desired.

While the invention has been described. with reference to a particular embodiment .100

thereof, various modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

6 1. A method of heat treating magnet steels, which consists in heating a magnet steel to a temperature above the critical temperature, and quenching the magnet steel in a medium heated to a temperature ranging 10 from approximately 200 F. to approximately 600 F.

2. A method of heat treating magnet steels, Which consists in heating a magnet steel to a temperature of approximately 1750 F., and slowly quenching the magnet steel in a medium heated to a tem erature ranging from approximately 200 to approximately 600 F.

3. A method of heat treating magnet steels,

which consistsin heating a magnet steel to a temperature above the critical temperature, and quenching the'magnet steel in a heated medium having a temperature of approximately 500 F.

4. A method of heat treating magnet steels, which consists in heating magnet steel to a temperature of approximately 17 50 F., and quenching the magnet steel in a heated me dium having a temperature of approximately In witness whereof, We hereunto subscribe our names this 10th day of January A. D.,

. KENNETH L. SCOTT. :l I ARTHUR L. KIRBY. MARION R. LEACH. 

